|
Interpreting the infrared
spectrum of 2,2-dimethylbutane
[Author
©
Dr WP Brown PhD:
Doc Brown's advanced level organic chemistry exam revision notes
suitable for students of UK A level chemistry courses & US K12 grade
11, grade 12 and AP honors chemistry courses: Molecular
spectroscopy - analysing the
infrared spectrum of
2,2-dimethylbutane
[updated
October 28th 2025]
email doc
brown
Re-edit
CH3CH2C(CH3)3
Links associated with 2,2-dimethylbutane
This is a BIG
website, PLEASE take time to explore it
Infrared spectroscopy - spectra index
See also
comparing infrared, mass, 1H NMR & 13C NMR
spectra of the structural alkane isomers of C6H14
Introductory note on the infrared spectrum of 2,2-dimethylbutane
Students and teachers please note
my explanation of the infrared
spectrum of 2,2-dimethylbutane is designed
for advanced, but pre-university, chemistry courses.
Based in
the infrared spectrum diagram for 2,2-dimethylbutane, only some of the most
prominent peaks for particular bond vibrations are discussed,
particularly if 2,2-dimethylbutane has a functional group with a particular
characteristic wavenumber peak.
The infrared spectrum of
2,2-dimethylbutane is
unique and the whole, or selected wavenumbers, can be used to
fingerprint its identity, sometimes analysing a mixture
containing 2,2-dimethylbutane or following its change of concentration in a
reaction.
Spectra obtained from a liquid film of 2,2-dimethylbutane. The right-hand part of the of the
infrared spectrum of 2,2-dimethylbutane, wavenumbers
~1500 to 400
cm-1 is considered the fingerprint region for the
identification of 2,2-dimethylbutane and most organic compounds. It is due to a unique set
of complex overlapping vibrations of the atoms of the molecule of
2,2-dimethylbutane.
2,2-dimethylbutane C6H14,
 ,
,
For more
see The molecular structure,
classification and
naming of alkanes
Interpretation of
the infrared spectrum of 2,2-dimethylbutane
The most prominent infrared absorption lines of
2,2-dimethylbutane
Strong C-H stretching vibration absorption bands at
wavenumbers 2940 to 2880 cm-1 for the CH2 and
CH3 groups in 2,2-dimethybutane.
Several strong C-H deformation vibration absorptions
at wavenumbers 1480 to 1365 cm-1 for the CH2
and CH3 groups in 2,2-dimethybutane.
Several strong C-C skeletal vibration
absorptions associated with a C-(CH3)3
group occur at wavenumbers 750 to 720 and 1255 to 1200 cm-1.
All of these infrared absorption vibrations are
characteristic of saturated alkyl structures in molecules, exemplified
by branched alkanes themselves e.g. 2,2-dimethylbutane.
The absence of other specific functional group bands
will show that particular functional group is absent from the
2,2-dimethylbutane
molecular
structure.
Key points
about the infrared spectrum of 2,2-dimethylbutane
2,2-Dimethylbutane shows a simple IR
spectrum dominated by alkane C–H stretching and bending vibrations,
with no functional group peaks.
Key IR Spectrum
Features of 2,2-Dimethylbutane
2,2-Dimethylbutane is
a highly branched alkane (C6H14) with no polar
functional groups. Its IR spectrum is characterized by:
-
Absence of
strong polar group absorptions
(e.g. no C=O, O–H, N–H)
-
Dominance of
C–H stretching and bending
typical of saturated hydrocarbons
-
Fingerprint
region complexity due
to multiple methyl groups and branching
Prominent
Wavenumbers Table
|
Vibration Type |
Approx. Wavenumber (cm⁻¹) |
Assignment |
|
C–H stretch
(sp³) |
2850–2960 |
Symmetric and
asymmetric stretching |
|
Methyl C–H
bend (umbrella) |
~1375 |
CH3
symmetric bending |
|
Methylene C–H
bend |
~1450 |
CH2
scissoring |
|
C–C skeletal
stretch |
800–1300 |
Weak, complex
fingerprint region |
|
Alkane
fingerprint peaks |
600–800 |
Multiple
overlapping skeletal vibrations |
Common
Misconceptions
-
“No peaks = no
information”: Students
may think the lack of strong peaks means the spectrum is useless. In
fact, the fingerprint region and C–H stretches are diagnostic for
alkanes.
-
Confusing CH3
and CH2
bends: The 1375 cm⁻¹
peak is often misassigned; it’s specific to methyl groups.
-
Assuming all
hydrocarbons show identical spectra:
Branching affects peak intensity and fingerprint complexity.
Exam Revision
Tips
These apply across AQA,
Edexcel, OCR, WJEC, CCEA, CIE, IB HL/SL, and US AP Chemistry:
What to Emphasize
-
Recognize alkane
IR patterns: C–H stretches
(2850–2960 cm⁻¹) and methyl bends (~1375 cm⁻¹)
-
Absence of
functional group peaks: No
C=O, O–H, N–H → confirms hydrocarbon
-
Use fingerprint
region for structural comparison:
Especially in multi-choice or matching spectra questions
Strategic Tips
-
Compare with
known spectra:
Practice distinguishing alkanes from alcohols, ketones, and
aromatics
-
Use
elimination logic: If
no polar group peaks are present, rule out
oxygen/nitrogen-containing compounds
-
Link IR to
molecular structure:
For 2,2-dimethylbutane, expect more CH₃-related vibrations due to
branching
Practice Prompts
-
“Explain why the IR
spectrum of 2,2-dimethylbutane lacks a peak at ~1700 cm⁻¹.”
-
“Identify the compound
from its IR spectrum showing peaks at 2960, 1450, and 1375 cm⁻¹ but
no polar group absorptions.”
|
Comparing the infrared, mass, 1H NMR and 13C NMR
spectra of the five structural alkane isomers of C6H14
NOTE: The images are linked to their
original detailed spectral analysis pages AND can be doubled in
size with touch screens to
increase the definition to the original hexane,
2-methylpentane, 3-methylpentane, 2,2-dimethylbutane and
2,3-dimethylbutane image sizes. These five molecules
are structural isomers of saturated alkanes of molecular formula C6H14
and
exemplify the infrared, mass, 1H NMR and 13C NMR spectra of lower
aliphatic alkanes (non-cyclic alkanes). |
|
Infrared spectra below. |
 |
 |
 |
INFRARED SPECTRA:
Apart from the significant differences in the fingerprint region at
wavenumbers 1500 to 400 cm-1, there are no other
great striking differences, but each could be identified from
its infrared spectrum.
All the absorption
bands are typical of molecules containing saturated alkyl structure and
there are no characteristic infrared absorptions due to a specific
functional group. |
|
|
 |
|
Infrared spectra above, mass spectra below. |
 |
 |
 |
MASS SPECTRA: Base ion
peaks plus m/z comments.
Hexane: m/z 57, 42 and 56 prominent
2-methylpentane: m/z 43, 42 and 71 prominent
3-methylpentane: m/z 57, 41 and 56 prominent
2,2-dimethylbutane: m/z 43, 41, 57 and 71
prominent
2,3-dimethylbutane: m/z 43, 41, 42 and 71
prominent |
 |
 |
|
Mass spectra above, 1H NMR spectra below. |
 |
 |
 |
1H NMR SPECTRA: They can
all be distinguished by their different integrated proton ratios -
need very high resolution.
Hexane:
3 1H
δ shifts, H ratio 3:2:2 (6:4:4 in formula)
2-methylpentane:
5 1H
δ shifts, H ratio 6:3:2:2:1
3-methylpentane:
4 1H
δ shifts, H ratio 6:4:3:1
2,2-dimethylbutane: 3 1H
δ shifts, H ratio 9:3:2
2,3-dimethylbutane: 2 1H
δ shifts, H ratio 6:1 (12:2 in formula) |
 |
 |
|
1H NMR spectra above, 13C NMR spectra below. |
 |
 |
 |
13C NMR SPECTRA: From the
number of shifts, you can't distinguish (iii) and (iv) but you can
distinguish them from (i), (ii) and (v). (i) Hexane: 3 13C
δ shifts
(ii) 2-methylpentane: 5 13C
δ shifts
(iii) 3-methylpentane: 4 13C
δ shifts
(iv) 2,2-dimethylbutane: 4 13C
δ shifts
(v) 2,3-dimethylbutane: 2 13C
δ shifts |
 |
 |
|
13C NMR spectra above. |
Key words & phrases: image and diagram explaining the infrared spectrum
of 2,2-dimethylbutane, complete infrared absorption spectrum of
2,2-dimethylbutane, comparative spectra of
2,2-dimethylbutane, prominent peaks/troughs for identifying functional groups in the infrared spectrum of
2,2-dimethylbutane,
important wavenumber values in cm-1 for peaks/troughs in the infrared spectrum
of 2,2-dimethylbutane, revision of infrared spectroscopy of 2,2-dimethylbutane, fingerprint region analysis of
2,2-dimethylbutane, how to identify 2,2-dimethylbutane from its infrared spectrum, identifying organic
compounds like 2,2-dimethylbutane from their infrared spectrum,
how to analyse the absorption bands in the infrared spectrum of
2,2-dimethylbutane detection of
functional groups in the 2,2-dimethylbutane molecule example of the infrared spectrum of a
molecule like 2,2-dimethylbutane with a functional group interpreting interpretation of the infrared spectrum of 2,2-dimethylbutane
Diagram of absorption of wavenumber
peaks in the infrared spectrum of 2,2-dimethylbutane. Characteristic peak wavenumbers in the infrared
spectrum of 2,2-dimethylbutane. Finger print identification pattern using the infrared
spectrum of 2,2-dimethylbutane. Revision notes on the infrared spectrum of
2,2-dimethylbutane. Matching
and deducing the structure of the 2,2-dimethylbutane molecule from its infrared
spectrum. Infrared spectroscopy of aliphatic
alkanes, infrared spectra of
2,2-dimethylbutane, a structural isomer of molecular formula C6H14 How do you interpret the infrared absorption spectrum of
2,2-dimethylbutane How
to interpret the infrared spectrum of 2,2-dimethylbutane Explanatory diagram of the
infrared spectrum of the 2,2-dimethylbutane molecule in terms of its molecular
structure. Listing data of the prominent main wavenumber peaks
troughs in the infrared spectrum of 2,2-dimethylbutane. How to explain the infrared
spectrum of 2,2-dimethylbutane. Use of the infrared spectrum of
2,2-dimethylbutane, identification
of 2,2-dimethylbutane from its infrared spectrum - fingerprint wavenumber pattern
to identify the 2,2-dimethylbutane molecule. The uses of the infrared spectrum of
the 2,2-dimethylbutane molecule. The distinctive features of the infrared spectrum
of the 2,2-dimethylbutane molecule explained interpretation diagram explaining the
peaks-trough of the transmittance of the infrared spectrum of
2,2-dimethylbutane
what does the infrared spectrum tell you about the structure and
properties of the 2,2-dimethylbutane molecule? How is infrared spectrum of
2,2-dimethylbutane used
to identify 2,2-dimethylbutane?
Links associated with 2,2-dimethylbutane
The chemistry of ALKANES
revision notes INDEX
The mass spectrum of
2,2-dimethylbutane
The H-1 NMR spectrum of
2,2-dimethylbutane
The C-13 NMR spectrum of
2,2-dimethylbutane
Infrared spectroscopy index
ALL SPECTROSCOPY INDEXES
All Advanced Organic
Chemistry Notes
Use My Google search site box
Email doc b:
chem55555@hotmail.com
Website content © Dr
Phil Brown 2000+. All copyrights reserved on revision notes, images,
quizzes, worksheets etc. Copying of Doc Brown's pre-university
advanced level chemistry website material is NOT
permitted. Exam revision summaries & references to science course specifications
are unofficial. These organic chemistry revision notes on
spectroscopy are
suitable for use of pre-university students studying AQA advanced level
chemistry, Edexcel advanced level chemistry, OCR advanced level
chemistry, IB advanced level chemistry, WJEC (Eduqas) advanced level
chemistry, CIE advanced level chemistry, US grade 11-12 AP honors
chemistry courses and they will also prove useful to
1st year undergraduate students of chemistry. |
